1. Field of the Invention
The present invention concerns a switching system architecture with improved growth characteristics. This architecture can be used for time or space division switching. The system can be expanded between a hundred and several tens of thousands subscriber lines with only one basic equipment. This equipment is an elementary nodal switching network or a node containing all the hardware involved during a call. A node can carry calls from (or to) its own terminals and transit calls from other nodes. Each node is linked with the same limited number of other nodes through internodal links and during growth additions a small number of links are changed. Hardware troubles are limited to one node and little or none affect the overall blocking characteristics of the network.
Each elementary nodal switching network is capable of handling with its own subscriber and trunk traffic together with the internodal traffic. This nodal structure is therefore very different from the graded structure of the specialized switching stations which form the conventional telecommunication network with their different switching levels: satellite exchange, central exchange, toll exchange, transit exchange, international exchange, . . . and from the graded structure in the switching units: proper in which the subscriber selection stage and the group selection stage have different functions.
The advantages of a nodal structure of identical elementary nodal switching networks over a conventional switching network system are the following:
It is possible to attain a high rate up to 100 of the maximum to the minimum capacity of the switching network unit formed by the elementary nodal switching networks;
Capacity extensions can be made by small increases, say of 1% of the old capacity without noticeably changing the structure of the system already built;
Breakdown in a node only affects a limited number of subscriber lines or trunks.
2. Description of the Prior Art
A three-dimensional nodal structure for a switching network unit has already been proposed in the two publications: "Comparison of Different Connecting Networks: Grid Connecting Networks and its Control with Microprocessors" by K. RAHKO, International Conference on Communications, Vol. II, Pages 22-15 to 22-19, San Francisco, June 16-18, 1975 and "Nodal Switching Networks"by A. E. JOEL, International Telegraphic Congress, Pages 312-1 to 312-8, Stockholm, 1973. Switching nodes are arranged in rows and in superimposed planes. The number of internodal links ending at each node is the same for all nodes and the mean distance between one node and all other nodes is the same whichever the node (the term "distance" signifies the number of nodes inserted between an incoming and an outgoing nodes). This is obtained by connecting either the nodes of the last row of each plane to the nodes of the first row of said plane or the nodes of the last plane to the nodes of the first plane.
In the prior art arrangements, extension of the switching network capacity is only possible row by row or plane by plane. Extension node by node is not allowed by these arrangements.